1. Field of the Invention
This invention relates to an image signal processing device for processing an image signal.
2. Description of the Related Art
The conventional image signal processing apparatuses include an electronic still video camera system.
In the electronic still video camera system, a video camera part is arranged to form an image signal corresponding to the image of an object to be photographed. The image signal is recorded on a recording medium such as a magnetic disc or the like. The image signal recorded on the recording medium is reproduced to have an image corresponding to the image signal either displayed on a monitor device or printed by a printer.
The recording device of the electronic still video camera system separates one field portion of the image signal obtained by the video camera part into a luminance signal and a chrominance signal. The luminance signal is frequency-modulated into a frequency-modulated luminance signal. The chrominance signal is frequency-modulated into a frequency-modulated color-difference line-sequential signal after being converted into a color-difference line-sequential signal as well known. The frequency-modulated luminance signal and the frequency-modulated color-difference line-sequential signal are frequency-multiplexed to form a recording signal. The recording signal thus obtained is recorded in one recording track on the recording medium. Further, in recording one frame portion of the image signal on the recording medium, two field portions of the recording signal corresponding to two field portions of the image signal which jointly form one frame portion of the image signal are recorded in two recording tracks on the recording medium.
There is provided an index signal (hereinafter referred to as ID signal for short) for indicating the image recording date including the year, month and day or recording time including the hour, minute and second, or the like. The ID signal is frequency-multiplexed with the recording signal. Further, the ID signal is formed, as well known, by DPSK (differential phase shift keying) modulating a given single frequency signal of a frequency 13fH (fH: horizontal scanning frequency) with digital data which indicates the above-stated recording date or recording time or the like.
The frequency spectrum of the recording signal recorded on the recording medium in the above-stated manner is shown in FIG. 2 of the accompanying drawings. In FIG. 2, a reference numeral 31 denotes the ID signal; 32 denotes the frequency-modulated color-difference line-sequential signal; and 33 the frequency-modulated luminance signal.
FIG. 1 shows in outline the arrangement of a reproducing device included in the electronic still video camera system. Referring to FIG. 1, a magnetic disc 2 is arranged to be rotated by a motor 1 at a given rotation cycle. With the disc 2 thus rotated, a signal recorded is reproduced from the disc 2 by a magnetic head 3. The reproduced signal is amplified by a pre-amplifier 4. After that, the frequency-modulated luminance signal is separated by a high-pass filter (HPF) 5. The frequency-modulated color-difference line-sequential signal is separated by a band-pass filter (BPF) 6. Further, the ID signal is separated by another BPF 7.
The frequency-modulated luminance signal which has been separated by the HPI 5 is supplied to an equalizer 8 to have its frequency characteristic corrected. A luminance signal frequency demodulation circuit 9 frequency-demodulates the frequency-modulated luminance signal to a baseband luminance signal.
The baseband luminance signal which has been output from the luminance signal frequency demodulation circuit 9 is supplied to a drop-out compensation circuit 10 to be compensated for its drop-out part generated during the process of reproduction. The drop-out-compensated luminance signal is supplied both to a skew compensation circuit 11 and a synchronizing signal separation circuit 12.
The synchronizing (hereinafter referred to as sync for short) signal separation circuit 12 separates horizontal and vertical sync signals from the baseband luminance signal output from the drop-out compensation circuit 10. These sync signals are supplied both to a DPSK demodulation circuit 13 and a sync signal generating circuit 14. The horizontal and vertical sync signals separated by the sync signal separation circuit 12 have a skew, as well known, in a field reproduction mode, in which the signal recorded in one recording track on the magnetic disc 2 is repeatedly reproduced. The sync signal generating circuit 14 is arranged to generate sync signals of varied kinds in synchronism with the horizontal and vertical sync signals separated by the sync signal separation circuit 12.
The baseband luminance signal which has been supplied from the drop-out compensation circuit 10 to the skew compensation circuit 11 is compensated for a skew occurring in the baseband luminance signal in the field reproduction mode as mentioned above. The skew compensation circuit 11 thus performs skew compensation in such a way as to keep the continuity of the horizontal sync signal added to the baseband luminance signal. After passing through the skew compensation circuit 11, the luminance signal is supplied both to a character signal addition circuit 15 and a sync signal separation circuit 16.
The sync signal separation circuit 16 is arranged to separate the horizontal and vertical sync signals from the baseband luminance signal which has been skew compensated by the skew compensation circuit 11. The horizontal and vertical sync signals separated by the sync signal separation circuit 16 are supplied to a character signal generating circuit 17. The character signal generating circuit 17 is arranged to generate a character signal according to the contents of the ID signal which has been supplied from the DPSK demodulation circuit 13 as will be further described later on. The character signal generated by the character signal generating circuit 17 is supplied to the above-stated character signal addition circuit 15. The character signal addition circuit 15 is arranged to add the character signal generated by the character signal generating circuit 17 to the skew-compensated baseband luminance signal output from the skew compensation circuit 11. The output of the character signal addition circuit 15 is supplied both to a multiplex circuit 18 and an output terminal 19.
Meanwhile, the frequency-modulated color-difference line-sequential signal which has been extracted by the BPF 6 is supplied to an equalizer 20 for correction of its frequency characteristic. After that, the color-difference line-sequential signal is frequency-demodulated by a color-difference line-sequential signal frequency demodulation circuit 21 into a baseband color-difference line-sequential signal. The baseband color-difference line-sequential signal output from the color-difference line-sequential signal frequency demodulator circuit 21 is supplied to a skew compensation circuit 22 to be compensated for a skew occurred therein during the process of field reproduction. The skew-compensated color-difference line-sequential signal is then supplied to a simultaneous conversion circuit 23 to undergo a simultaneous converting process. As a result, the simultaneous conversion circuit 23 outputs two color-difference signals R-Y and B-Y and supplies them to a quadrature two-phase modulation circuit 24. The quadrature two-phase modulation circuit 24 then quadrature two-phase modulates the inputs into a carrier chrominance signal.
The carrier chrominance signal output from the quadrature two-phase modulation circuit 24 is supplied to a mute circuit 25. At the mute circuit 25, the carrier chrominance signal is muted during a period of time for which the character signal is added to the luminance signal by the character signal addition circuit 15 as mentioned above. The period of time for which the carrier chrominance signal is muted by the mute circuit 25 is controlled by a control signal supplied from the character signal generating circuit 17.
The carrier chrominance signal which has been muted by the mute circuit 25 during a period of time for which the character signal is added to the luminance signal is output not only from an output terminal 26 but also from another output terminal 27 as a television signal with the carrier chrominance signal frequency-multiplexed by the multiplex circuit 18 with the luminance signal to which the above-stated character signal has been added.
The DPSK-modulated ID signal which has been extracted by the BPF 7 is demodulated by a DPSK demodulation circuit 13 in synchronism with the horizontal and vertical sync signals which have been separated from the sync signal separation circuit 12 and which have not been skew compensated as yet. The demodulated ID signal is supplied to the character signal generating circuit 17. Upon receipt of the ID signal, the character signal generating circuit 17 generates, according to the content of the ID signal, a character signal which represents a character, a digit or a symbol as applicable.
However, the reproducing device arranged as shown in FIG. 1 has presented the following problem: During the field reproduction, at the skew compensation circuit 22 which skew-compensates for the color-difference line-sequential signal, there arises a discrepancy in level or hue between the color-difference line-sequential signal and a color-difference line-sequential signal which has been delayed for 1/2 horizontal synchronizing period for the purpose of using it for the skew compensation. This results in flickering or a color deviation of a reproduced image obtained though the skew compensation. Further, the device necessitates, as shown in FIG. 1, use of the horizontal and vertical sync signals for DPSK-demodulating the ID signal before the skew compensation thereof and thus necessitates the use of sync signal separation circuits in two channels. This not only requires a complicated circuit arrangement but also tends to result in a moire or the like caused by the generation of a cross-talk component between the sync signals on the reproduced picture plane as the sync signals separated by the sync signal separation circuits of different channels differ from each other.